Strange measurement

Thread Starter

Mullins

Joined Dec 31, 2021
172
Hi,
Today I have worked with an old diesel car. Since the car have some issue I made some measurement with my dmm. I post one picture to bette explain my case. When I put the probe on wire A and B I got:
2.5vcc
450hz
duty cycle 2%

When I put the probe between chassis ground and A wire I got:
12.5vcc
Frequency =0Hz


When I put the probe between chassis ground and B wire I got:pompa lucas epic.png
10 vcc.
Frequency =0Hz

This solenoid is a shut off valve he have non sense to control it with pwm. I sure he always need only on or off.

Is there any sense of my measurement?
 

Ya’akov

Joined Jan 27, 2019
9,150
It makes perfect sense.

A is 12.5V above the 0V chassis reference.
B is 10.0V above the 0V chassis reference.
A-B is the difference, 2.5V.
Using a PWM signal to manage valves on engines is common. You any be mistaken about the open-closed nature of the valve—it may be feathered by the ECM at points in the engine’s starting, stopping, or running cycles.
 

Ian0

Joined Aug 7, 2020
9,814
Hi,
Today I have worked with an old diesel car. Since the car have some issue I made some measurement with my dmm. I post one picture to bette explain my case. When I put the probe on wire A and B I got:
2.5vcc
450hz
duty cycle 2%

When I put the probe between chassis ground and A wire I got:
12.5vcc
Frequency =0Hz


When I put the probe between chassis ground and B wire I got:View attachment 310132
10 vcc.
Frequency =0Hz

This solenoid is a shut off valve he have non sense to control it with pwm. I sure he always need only on or off.

Is there any sense of my measurement?
What does the solenoid do? Is it the fuel shut-off valve?
Is it a non-common-rail diesel, where the speed control is a mechanical link to the injector pump? ("old" is a relative term, and we have had common-rail diesels for over 20 years now)
If it is the fuel shut-off valve, then I would not expect any other position than "open" or "closed"
 

Ian0

Joined Aug 7, 2020
9,814
I think that the readings are spurious.
Is one side of the valve permanently connected to the battery positive? And the other side grounded by the "engine stop" switch?
What do you get if you repeat the readings with a 1k resistors across the meter probes?
 
Top